This invention relates to a bipolar separator and, in particular, to a bipolar separator used in a fuel cell assembly.
In U.S. patent application Ser. No. 08/725,286, filed Oct. 2, 1996, assigned to the same assignee hereof, there is disclosed a bipolar separator which can be more simply and efficiently manufactured. As a result, the cost of the separator and, therefore, the fuel cell assembly, can be reduced.
More particularly, the bipolar separator of the '286 application comprises a clad of nickel and stainless steel formed as a plate in which troughs are provided into the nickel surface of the plate on the four sides of the plate. One set of opposing troughs is bent up and around so that the stainless steel surface faces outwardly to form a first set of opposing side rails. The second set of opposing troughs already have their stainless steel surfaces facing outwardly and form a second set of opposing side rails. The sets of side rails support electrolyte matrices when the separator plate is used to separate adjacent fuel cells of a fuel cell stack.
By forming the bipolar separator with troughs, the bending procedure is greatly simplified, as compared to the prior procedure used for earlier designs. This prior procedure required eight bending steps and an etching step to remove the outer facing nickel clad of one of the sets of side rails.
However, the bipolar separator of the '286 application also has certain disadvantages. Thus, each trough of the separator at the point of initial contact with the supported electrolyte matrix has an abrupt change in direction where the vertical and horizontal walls of the trough meet. This abrupt change creates a stress area which can cause cracks in the supported matrix. Cracks in the matrix, in turn, can result in cross-flow of the hydrogen and oxygen gases in the fuel cell assemblies, thereby seriously deteriorating fuel cell performance.
It is, therefore, an object of the present invention to provide a bipolar separator which does not suffer from the above disadvantages.
It is a further object of the present invention to provide a bipolar separator which has side rails configured to have reduced stress producing areas.